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Serving Alberta's Roofing Industry Since 1961

BUR Section 4: Vapour Retarders

BUR-4.1 General

.1

ARCA Warranty Ltd. requires the use of a vapour
retarder membrane for conventional or combination design built-up
roofing assemblies, when a Warranty Certificate is to be issued.
When a complete roof system, including the existing insulation is
being replaced, a vapour retarder is required for the issuance of
the Warranty Certificate.

.2

The selection of the type and quality of the
vapour retarder is a building design function and is the
responsibility of the design authority. When selecting the vapour
retarder membrane, the design authority should take into
consideration a number of factors such as building occupancy, air
conditioning, envelope seals and humidity levels during building
construction. Concrete pouring and drywall mudding after roof
installation may increase humidity design values.

.3

Upgrades to the minimum recommendations,
including self-adhering composite vapour retarders, shall be
installed as per membrane manufacturers written instructions.

Added

2014-10

.4

The vapour retarder specifications recommended
in this section are experience based for normal humidity
conditions, 40% at 21°C. For higher humidity conditions the
application of an additional ply of membrane or the use of a high
performance vapour retarder membrane is recommended.

BUR-4.2 Common Elements of
Application

.1

The vapour retarder membrane shall be joined and
sealed to the primary membrane at roof perimeters, vertical roof
junctions and at roof penetrations. The vapour retarder membrane,
or an extension of the membrane, shall wrap the insulation
components and shall extend out over the secondary insulation a
minimum distance of 150mm (6”) and be adhered to the surface
of the secondary insulation. Alternatively, the vapour retarder
membrane may be carried up and adhered to the vertical substrate a
minimum distance of 50mm (2") above the top edge of the cant
strip.

.2

Organic felt vapour retarders must not be left
unprotected when inclement weather or exceptional circumstances
prevent the complete application of the roof assembly. The top ply
of felt shall be protected with a uniform visible coating of
bitumen.

.3

The primary insulation must be mechanically
fastened to the structural deck when polyethylene vapour retarders
are specified.

BUR-4.3 Existing BUR Membranes as
Vapour Retarders

.1

The following procedure shall be employed when
the primary membrane from an existing BUR protected membrane
assembly is to be left in place and serve as the vapour retarder
membrane for a replacement conventional or combination design roof
assembly. The existing membrane shall be prepared by removing any
wet or deteriorated material, dust, dirt and debris. The complete
surface, including any exposed substrate, shall be covered with a
minimum of one (1) ply of No. 15 organic felt membrane adhered in a
full application of hot bitumen.

BUR-4.4 Minimum Recommended Vapour
Retarders for Wood Decks

As a guide, the following specifications provide
the minimum composition and application procedures for ARCA
Warranty Ltd. required vapour retarders. The vapour retarders are
categorized by the deck (substrate) type to which they will be
applied. Vapour retarder designations beginning with
“W” apply to wood decks, e.g. W-VR-1, “C”
designates concrete decks and “S” designates steel
decks, etc.

BUR-4.4.1 Specification W-VR-1 Normal Humidity Conditions

General

The direct application of hot bitumen to wood
decks is not permitted.

The vapour retarder membrane must be uniformly
attached to its substrate.

For high humidity conditions add a minimum of one
additional ply of No. 15 organic felt fully adhered into an
interply mopping of hot bitumen applied at the approximate rate of
1 kg/m2 (20 lbs/100 sq. ft).

Application

For the separator sheet, nail one ply No. 15
organic felt to wood deck using large head galvanized roofing nails
spaced at approximately 150mm (6”) centres for laps and
approximately 300mm (12”) centers for field of the sheet.

BUR-4.4.2 Specification W-VR-2 Normal Humidity Conditions

General

The direct application of hot bitumen to wood
decks is not permitted.

The vapour retarder membrane must be uniformly
attached to its substrate.

For high humidity conditions add a minimum of one
additional ply of No. 15 organic felt fully adhered into an
interply application of hot bitumen applied at the approximate rate
of 1 kg/m2. (20 lbs/100 sq. ft).

Application

For the vapour retarder, nail one ply kraft
laminate sheet to wood deck using large head galvanized roofing
nails spaced at approximately 150mm (6”) centers for laps and
approximately 300mm (12”) centers for the field of the sheet.
Alternatively a one (1) ply kraft laminate sheet may be adhered in
a full roller coating or in continuous ribbons of vapour retarder
adhesive applied to surface of wood deck. Vapour retarder adhesive
application rates shall be in accordance with adhesive
manufacturer’s recommended application rates.

Kraft laminate side laps shall be minimum 50mm
(2”) wide and end laps shall be minimum 150mm (6”)
wide. Laps shall be fully sealed with a continuous coating of
vapour retarder adhesive or be fully sealed in hot bitumen prior to
nailing.

BUR-4.4.3 Specification W-VR-3 Normal Humidity Conditions

General

The direct application of hot bitumen to wood
decks is not permitted.

The vapour retarder membrane must be uniformly
adhered to its substrate.

For high humidity conditions add a minimum of one
additional ply of No. 15 organic felt fully adhered into an
interply application of hot bitumen applied at the approximate rate
of 1 kg/m2 (20 lbs/100 sq ft).

Application

For the vapour retarder, nail one (1) ply asphalt
coated base sheet to wood deck using large head galvanized roofing
nails spaced at approximately 150mm (6”) centers for laps and
approximately 300mm (12”) centres for field of the sheet.

Laps shall be fully sealed with an application of
hot bitumen prior to nailing.

BUR-4.4.4 Specification W-VR-4 Normal Humidity Conditions

General

Self-adhesive vapour retarder membrane must be
uniformly adhered to the primed substrate.

Membranes with a HDPE (Polyethylene) surface are
not compatible with hot bitumen application of insulation.

Application

Membrane side laps shall be a minimum of 75mm
(3”) and end laps a minimum of 150mm (6”).

Apply uniform pressure over the entire membrane
surface with a roller. Offset end lap joints from adjacent rows a
minimum of 300mm (12”).

BUR-4.5 Minimum Recommended Vapour
Retarders for Concrete Decks

BUR-4.5.1 Specification C-VR-1 Normal Humidity Conditions

General

The vapour retarder membrane must be uniformly
adhered to its substrate.

For adhered roofing systems priming of the
concrete deck is recommended by ARCA to improve adhesion, but is
not a minimum requirement.

For high humidity conditions add a minimum of one
(1) additional ply of No. 15 organic felt fully adhered into an
application of hot bitumen applied at the approximate rate of
1kg/m² (20 lbs/100 sq. ft.).

Application

For new construction apply two (2) plies of No. 15
organic felt adhered in a full application of hot asphalt applied
at the approximate rate of 1kg/m2 (20lbs/100 sq. ft). For two (2)
ply applications, the felt side laps shall be minimum 483mm
(19”) wide and end laps shall be minimum 150mm (6”)
wide.

When re-roofing, apply one (1) ply No. 15 organic
felt in a full application of hot bitumen applied at the rate of 1
kg/m² (20 lbs/100 sq. ft.). Side laps shall be minimum 100mm
(4”) wide and end laps shall be minimum 150mm (6”)
wide. Laps shall be fully sealed in an application of hot
bitumen.

BUR-4.6 Minimum Recommended Vapour
Retarders for Steel Decks

BUR-4.6.1 Specification S-VR-1 Normal Humidity Conditions

General

The direct application of hot bitumen to steel
decks is not permitted.

The vapour retarder membrane must be uniformly
adhered to its substrate.

ARCA recommends that prior to vapour retarder
application that a continuous leveling surface be adhered to the
steel deck such as gypsum board. The leveling surface provides
support for the vapour retarder membrane, reduces deck deflection
and reduces damage to the vapour retarder membrane, see
Specification SG-VR-1.

For high humidity conditions add a minimum of one
additional ply of No. 15 organic felt fully adhered into an
interply application of hot bitumen applied at the approximate rate
of 1 kg/m2 (20 lbs/100 sq. ft). For two ply applications, the felt
side laps shall be minimum 483mm (19”) wide and end laps
shall be minimum 150mm (6”) wide.

Application

For the vapour retarder, apply one ply kraft
laminate sheet adhered in a full roller coating or in continuous
ribbons of vapour retarder adhesive applied parallel to the top
flanges of the steel decking. Adhesive application rates shall be
in accordance with adhesive manufacturer's recommended application
rates. Vapour retarder adhesive is produced in both winter and
summer grades, consult adhesive manufacturer for appropriate grade
and application rates required.

BUR-4.6.2 Specification S-VR-2 Normal Humidity Conditions

General

Self-adhesive modified bitumen membrane vapour
retarder application without a thermal barrier shall be in
compliance with the Alberta Building Code or Authorities Having
Jurisdiction should be consulted before installation.

Primer application is as per membrane
manufacturer's requirements.

Membranes with a HDPE (Polyethylene) surface are
not compatible with hot bitumen application of insulation.

Application

Membrane side laps shall be a minimum of 75mm
(3”) and end laps a minimum of 150mm (6”) and fully
supported. Offset end lap joints from adjacent rows a minimum of
300mm (12”).

Apply uniform pressure over the membrane surface
with a roller to enhance adhesion.

BUR-4.6.3 Specification SG-VR-1 Normal Humidity Conditions

General

The direct application of hot bitumen to steel
decks is not permitted.

The vapour retarder membrane must be uniformly
attached to its substrate.

For high humidity conditions add a minimum of one
additional ply of No. 15 organic felt fully adhered in an interply
application of hot bitumen applied at the approximate rate of 1
kg/m2 (20 lbs/100 sq ft). For two ply applications, the felt side
laps shall be minimum 483mm (19”) wide and end laps shall be
minimum 150mm (6”) wide.

When using drywall screws for attaching the gypsum
board auxiliary leveling surface, use a minimum of twenty (20)
screws per 1200mm x 2400mm (4 x 8’) sheet or a minimum of six
(6) screws for a 600mm x 1200mm (2 x 4’) sheet. Follow
Factory Mutual (FM) requirements when using screws with plates.

Application

For the vapour retarder, apply one ply No. 15 felt
fully adhered to the gypsum board in a full application of hot
bitumen applied at the approximate rate of 1 kg/m2 (20 lbs/100 sq
ft).

BUR-4.6.4 Specification SG-VR-2 Normal Humidity Conditions

General

Membranes with a HDPE (Polyethylene) surface are
not compatible with hot bitumen application of insulation.

Application

Membrane side laps shall be a minimum of 75mm
(3”) and end laps a minimum of 150mm (6”). Offset end
lap joints from adjacent rows a minimum of 300mm (12”).

Apply uniform pressure over the entire membrane
surface with a roller to enhance adhesion.

BUR-4.7 Minimum Recommended Vapour
Retarders for Bituminous Fills

BUR-4.7.1 Specification BF-VR-1 Normal Humidity Conditions

General

The vapour retarder membrane must be uniformly
adhered to its substrate.

For adhered roofing systems priming of the
bituminous fill is recommended by ARCA to improve adhesion, but is
not a minimum requirement.

For high humidity conditions add a minimum one (1)
additional ply of No. 15 felt fully adhered into an application of
hot bitumen applied at the approximate rate of 1 kg/m² (20
lbs/100 sq. ft.). For two (2) ply applications, the felt side laps
shall be minimum 483mm (19”) wide and end laps shall be
minimum 150mm (6”) wide.

Application

For new construction, apply two (2) plies of No.
15 organic felt in a full application of hot bitumen applied at the
approximate rate of 1 kg/m² (20 lbs./100 sq. ft.).

For two (2) ply applications the felt side laps
shall be minimum 483mm (19”) wide and end laps minimum 150mm
(6”) wide. Laps shall be sealed in an application of hot
asphalt.

When re-roofing, apply one (1) ply of No. 15
organic felt adhered in a full application of hot asphalt applied
at the approximate rate of 1kg/m2 (20 lbs/100 sq. ft.) per
mopping.

Side laps shall be minimum 100mm (4”) wide
and end laps shall be minimum 150mm (6”) wide. Laps shall be
fully sealed in an application of hot bitumen.